This invention relates generally to voltage monitoring apparatus and is concerned more particularly with a voltage sensing network having frequency compensating means.
In the operation of a conventional X-ray tube, for example, high magnitude voltages relative to electrical ground are applied to the cathode and anode electrodes in order to establish a strong electrostatic field therebetween. As a result, electrons emitted from the cathode are beamed electrostatically onto a small focal spot area of the anode with sufficient energy to generate an X-ray beam which emanates from the tube. Accordingly, the respective values of the voltages applied to the cathode and anode electrodes of the tube are directly related to the energy of the X-radiation thus generated.
It is well known that an X-ray beam may be passed through a selected portion of a patient for a short interval of time to obtain a shadow image of the internal body structure. Consequently, in order to ascertain the energy of X-radiation to which the patient is exposed, it is necessary to determine accurately the respective potentials of the cathode and anode electrodes during the exposure interval. Generally the peak voltage applied to the anode during the exposure pulse interval is provided by a peak reading voltmeter connected across a load resistive element in the external cathode-to-anode circuit. However, a peak reading voltmeter does not include means for evaluating the output voltage pulse waveform or for detecting voltage transients which could provide information concerning defects in the tube or in the external circuitry.
The output voltage waveform may be studied by connecting an oscilloscope across a portion of a voltage divider which is connected externally between the cathode and anode of the X-ray tube. However, if the resistive value of the voltage divider element is too low, overheating results. On the other hand, if the resistive value of the voltage divider element is too high, high frequency transients are not disclosed due to the effects of stray capacitance.
Therefore, it is advantageous and desirable to provide a voltage monitoring apparatus having means for evaluating a high voltage waveform and disclosing the presence of high frequency transients.